The use of refractory fiber block insulations as thermal insulating liners for various types of ovens, kilns and furnaces (particularly those used for annealing of articles such as glassware of firing of materials such as clay products) has become quite widespread in industry. These block insulations are lightweight, highly resistant to thermal shock, have very low heat holding capacities, and are readily installed and easily removed for repair or replacement. Generally the blocks are formed from refractory fiber blankets or batts, either by cutting the blankets or batts into small sections and placing these sections against one another to form the block, or by folding lengths of blankets into blocks. Each block commonly has width and breadth dimensions of approximately 1 ft. (30 cm) each with a depth in the range of from 4 to 12 in. (10 to 30 cm) depending on the amount of temperature drop to be obtained across the depth of the insulation. The blocks are mounted in parquet or checkerboard fashion on the inner wall of a furnace by such means as bolting, stud welding or the like, utilizing mounting brackets mounted on the back of the blocks. Such a parqueting arrangement is shown in FIG. 1. Typical of such block insulations is a system which has proved highly successful in commercial use; the block structure is described in U.S. Pat. No. 4,001,996 to C. O. Byrd, Jr. and the system is commercially available under the trademark Z-BLOK from Johns-Manville Corporation and its licensees.
To date, however, such block insulation systems have found their principal acceptance as insulating liners for gas-fired furnaces rather than for electrically heated furnaces. This is because gas-fired furnaces operate by directing the gas flames through ports in the side of the furnace wall. It has been a simple matter to leave appropriate openings in the fiber block insulation liner through which the gas ports can be extended, as shown in FIG. 1. A cementitious or loose bulk fiber insulation can then be used to fill the space between the gas duct and the next adjacent insulation blocks.
In electrically heated furnaces, however, the electrical heating elements must be mounted on the inside of the furnace and particularly inwardly of the thermal insulation layer. Where the thermal insulation layer is constructed or refractory firebrick or high density rigid refractory fiberboard, specially constructed electrical heating support hangers may be incorporated directly into the rigid wall structure as it is constructed; see, e.g., U.S. Pat. No. 3,987,237. Because of the fundamental differences between the fibrous structures of the insulating blocks (which, as noted, are made from batts and/or blankets of fibers) and the rigid board or brick insulations, however, the systems for electrical heater element support used with the latter have not in practice been adaptable to use with the block insulations.
Two different approaches to providing for electrical heater element supports for fibrous insulation lined furnaces have been described in the prior art. In one system, individual metal hooks for each heater element loop penetrate the fiber and are secured to a metal rod disposed in the fiber body. Such a system is undesirable because each metal hook serves as a heat loss path through the insulation. The portions of the metal rods which protrude from the hot face of the insulation also are susceptible to thermal degradation and act to limit the temperature at which the furnace can be operated unless costly high temperature metal alloys are used for the rods. In the other system, disclosed in U.S. Pat. No. 3,705,253, the fibrous insulation is completely faced with ceramic panels which are secured through the insulation directly to the wall of the furnace. The panels completely cover the hot face of the insulation and have support hooks for the heater elements protruding from the hot face of the panels. This system is undesirable because it requires costly and heavy ceramic panels and because it essentially negates the benefits of the use of fibrous insulation. The ceramic panels suffer all the dificiencies of rigid brick walls (spalling, cracking, high heat capacity, thermal shock susceptibility, etc.) and they block the much more versatile fibrous material from serving as the hot face insulation and thus avoiding such problems.
It is therefore an object of the present invention to provide a system and apparatus such that fiber block insulations can be conveniently and easily used as the predominant thermal insulating liner for electrically heated furnaces.
It is also an object of this invention to provide a system and apparatus for supporting electrical heating element means directly in association with ceramic fiber block insulations.
It is further an object of this invention to provide a system and apparatus in which ceramic fiber insulation and electrical heater element support means are combined into a unitary device.
It is also an object of this invention to provide a system and apparatus in which the principal hot face insulation is fibrous and wherein no metal (other than the heater elements) need be subject to the full furnace temperature.